Water Polarity and Molecular Structure

Water Polarity and Bonding

• Water (H₂O) has a bent molecular shape, contributing to its unique properties.
• Oxygen's electronegativity causes the oxygen atom to have a partial negative charge, and hydrogen atoms a partial positive charge.
• Unequal sharing of electrons leads to a dipole moment, with one end being slightly negative and the other slightly positive.
• Polarity enables water to form hydrogen bonds, which are fundamental for high boiling points and solubility.

Types of Water Bonds

• Hydrogen Bonds: Weak attractions between the slightly positive hydrogen of one water molecule and the slightly negative oxygen of another, impacting properties like surface tension.
• Polar Covalent Bonds: Unequal sharing of electrons between hydrogen and oxygen within the water molecule, contributing to its polar nature.
• Ionic Interactions: Water surrounds and separates ions in ionic compounds, aiding in dissolving substances and acting as a universal solvent.

Functions of Water in the Human Body

• Water acts as a proton donor (acid) and plays a role in maintaining acidity in solutions.
• Essential for forming peptide bonds in protein synthesis.

Carbohydrates Overview

• Monosaccharides: Single sugar units like glucose (energy source), fructose (sweeter, found in fruits), and galactose (part of lactose).
• Disaccharides: Combinations of monosaccharides, e.g., sucrose (table sugar), lactose (milk), and maltose (from starch digestion).
• Oligosaccharides: Short chains of sugar units such as raffinose found in beans and vegetables.
• Polysaccharides:
  • Starch (glucose storage in plants, e.g., potatoes).
  • Glycogen (glucose storage in animals, mainly in liver and muscles).
  • Cellulose (structural component of plant cell walls, not digestible by humans).

Composition of Carbohydrates

• Composed mainly of carbon (C), hydrogen (H), and oxygen (O) with a typical H:O ratio of 2:1.

Dehydration Synthesis vs. Hydrolysis

• Dehydration Synthesis: Removes a water molecule to join smaller molecules into larger ones, like forming disaccharides from monosaccharides.
• Hydrolysis: Adds a water molecule to break larger molecules into smaller units, as seen in starch breaking down into glucose.

Examples of Disaccharides

• Sucrose: Glucose + Fructose; common table sugar.
• Lactose: Glucose + Galactose; found in milk.
• Maltose: Two glucose units; found in malted foods.

Glycogen vs. Starch

• Both serve as glucose storage, but glycogen is used in animals while starch is used in plants.

Enzyme Functionality and Activation Energy

• Substrate Binding: Specific active sites on enzymes accommodate substrates to form enzyme-substrate complexes.
• Induced Fit: Enzymes may change shape upon binding to enhance interaction.
• Catalysis Mechanisms: Enzymes lower activation energy, allowing reactions at lower temperatures and faster rates.
• Product Release: Following reactions, products are released and enzymes return to initial state.

Factors Hindering Enzyme Activity

• Denaturation: Extreme temperatures or pH levels can alter enzyme structure.
• Inhibition: Competitive (blocking active site) and non-competitive (changing shape) inhibition reduce effectiveness.
• Cofactor/Coenzyme Availability: Lack of necessary helpers can inhibit enzyme function.

Nucleus and Nucleolus Functions

• Nucleus: Largest organelle, stores DNA and nucleoplasm, site of DNA replication and transcription.
• Nucleolus: Produces rRNA and assembles ribosomal subunits crucial for protein synthesis.

Passive Transport Examples

• Diffusion: Movement from high to low concentration (e.g., gas exchange).
• Facilitated Diffusion: Uses proteins to help molecules cross membranes (e.g., glucose).
• Osmosis: Water movement across semipermeable membranes.
• Filtration: Movement driven by hydrostatic pressure (e.g., kidney filtration).

Active Transport Examples

• Sodium-Potassium Pump: Transports Na⁺ out and K⁺ into cells, utilizing ATP.
• Proton Pump: Moves protons across membranes, important for digestion.
• Endocytosis: Cell membrane engulfs materials to form vesicles; includes phagocytosis (large particles) and pinocytosis (liquids).
• Exocytosis: Vesicles release contents outside the cell.

Active vs. Passive Transport Differences

• Energy Requirement: Active transport requires energy (ATP), passive does not.
• Direction of Movement: Active transport moves against gradients, while passive moves with gradients.
• Types of Transport: Active includes pumps and vesicular transport; passive includes diffusion and osmosis.
• Specificity: Active transport is often specific to certain substances; passive is less selective.

Factors Affecting Rate of Diffusion

• Concentration Gradient: Greater differences enhance diffusion speed.
• Temperature: Higher temperatures increase molecular movement.
• Molecular Size: Smaller molecules diffuse faster.
• Medium: Gases diffuse quicker than liquids; liquids quicker than solids.
• Surface Area: Larger areas increase diffusion potential.
• Distance: Shorter distances facilitate rapid movement.

Solvent vs. Solute

• Solvent: Dissolves solutes, usually present in greater amounts (e.g., water).
• Solute: Dissolved in solvent, present in lesser amounts (e.g., salts).
• Movement in Osmosis: During osmosis, the solvent (water) moves to balance solute concentrations across membranes.

Osmotic Environments

• Isotonic: Equal solute concentrations; no net movement.
• Hypotonic: Lower solute concentration outside; water moves in, possible cell bursting.
• Hypertonic: Higher solute concentration outside; water moves out, causing cell shrinkage.